I have a ZKK602 375H&H and a CZ550 'Magnum' (so marked on side of reciever) in 416Rigby. Both extractors look the same and function exactly alike. As the round is withdrawn from the magazine by the bolt the rim enters the extractor as soon as the round starts to leave the magazine,ie: as soon as the rails release it to rise into the extractor. This means the rim is completely under the extractor for at least half the length of the case. I don't know how much more 'controlled' the round could be. Only other model I have used was a ZKK 601,I believe, in 308 and it functioned the same as mine. Have never seen any other smaller caliber 550's and as I said mine is MARKED 550 MAGNUM so maybe the extractor is different on the smaller calibers but if so I can can see no need for it to be so. The only thing I have done to mine is modify the follower as David Miller does to allow the last round to feed better. This just means grind the ridge on the follower back so the round is released on the left side as soon as it clears the rail on the right side. It's only a problem on the last round and is the same for any follower fed magazine in any gun. I will have to check out smaller caliber 550's next time I'm in a shop. I would expect the extractor to be the same on all magnum cases but it may not be.